The immediate outcome would be a larger distinction between Romania* : people tend to forget that western provinces weren't that prosperous after the IIIrd century crisis, safe for Africa, Spain and parts of Italy, or even this much Roman (Adrian III passed actually more time fending off Mauri incursions than dealing with Fulgens' usurpation in Africa).
While Romania managed to salvage what it could (at the cost of giving up provincial administration to Romano-Barbarians militia) IOTL, ITTL, without the permanance of a Roman state to hold it together, we could witness an actually worse situation for Europe : I doubt you'd have enough structures to really allow the usual super-kingdom build-up you had in Balkans and Syria, so no Gothic or Alemanic hegemony (would it be temporarily) to provide a smooth transition to post-classical world; and rather an ensemble of "provincial" kingdoms on which WRE (probably shrinking to be an "imperial" kingdom of Italy) would have little to no direct control on.
I know that on this board there's a tendency to say that, because it would be richer (which isn't that obvious on the long term, while truer in a first time), ERE would be able to at least swallow up part of the WRE (or what would remain of it) but the Sassanian pressure isn't going anywhere, even if I could see Gepid Mosesia or Lombard Illyricum (if ERE survives weakened) or ERE directly being able to push back (at a cost) pontic chiefdoms.
Eventually, we could see a growing gap economically and politically between West and East, especially if the ERE manages to do what Barbarian kingdoms did by captating Vistulian and Baltic trade (There's the argument that Barbarians managed to do so and make Constantinople, Thebes and Sinope trade hubs because of their historical relation with these zones, and maybe "western Barbarians" could pull it, but it strikes me as shoehorned as Barbarians were eventually heavily hellenized peoples), depriving Barbarian kingdoms from a clear commercial edge (maybe an African or North Sea trade? But if ERE manages to pull an WRE, they would have trouble to do so).
On the other hand we could have been spared the comparison between the post-classical Roman Empire and the Shogunate (I'm looking at you, Imperial Rule II or any Contrarian Interactive game for that matter), and the cliché about how Greeks lost civic mindset and being cowards submitting to Barbarians, so it's not that of a bad TL on this regard.
@SealTheRealDeal
Suebi (on which the Suebi element was more or less surrounded by other peoples, and that wouldn't ask much for having a PoD where Suebeland is called Frakland or Saxland) were more or less pushed back by Romano-Alemanic armies, with the idea of conquering back Britain that was let to herself before Gaelic takeover. It kinda backfired, but without Roman withdrawal and "strong motivation" from Romans (the carrot being subsides and land, the stick being...a stick), I don't think they would have been able to pull this and to swallow up the Roman statelets in Britain.
Eventually, we might have witnessed a weird mix in post-imperial Britain, with Gaels, Brittons, Romans and maybe some Germans (probably Franks or Saxons) : apart what happened in Moesia, with the Gepid/"Sarmatian"/Causasian/Turkic mix, quickly tookover by Goths, I'm not sure you'd have an IOTL equivalent.